from 1541 Ultimate homepage:

It is about time to release some news about the 1541U-II. I think some of you must be really curious about the extra features and possibilities that the 1541U-II give, and about the progress on production and firmware. To start off with the 1541U-II features, I can tell you that it differs from the ‘standard’ 1541U Plus/Ethernet that:

• the board itself is about 30% smaller than the 1541U;
• it has a MicroSD connector, instead of a full-size SD;
• it has a real-time-clock function, for correct file time and date;
• it has a larger FPGA, which enables the implementation of more features;
• it has a USB Host port, which can be used to connect USB-sticks;
• it is targeted to have a suitable case for the device.

Some of you have written in the forums, that the MicroSD connector is not much of an improvement. But the rationale behind going to MicroSD is mainly the available space on the board is less, and that with the addition of a USB-A port, the average user will use the usb-stick rather than the SD-card.

So the MicroSD-card does not need to be removed from the cartridge very often. However, because at the moment that I announced the 1541U-II, the USB port was not yet tested, I could not reveal this feature as I did not want to make promises that I can’t keep.

The USB turns out to be quite a bit of work to get it to work, but I can now announce that I managed to implement enough of a host-controller function to be able to talk to USB devices and send the most basic commands to access a mass-storage device. I am quite close to have implemented the ‘read-block’ and ‘write-block’ functions, which is the interface level that the file system module uses. In other words, I expect to be able to access the (FAT) file-system on the USB stick quite soon!

How will it work for the user? My objective is to have one ‘directory’ level above the current root of the SD-card, where you can select which partition you want to browse. There the USB flash drive becomes visible, as well as the MicroSD card, if present.

source: 1541ultimate.net